leetcode-86. Partition List

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None


class Solution(object):
    def partition(self, head, x):
        """
        :type head: ListNode
        :type x: int
        :rtype: ListNode
        """
        
        h1=l1=ListNode(None)
        h2=l2=ListNode(None)
        
        while head:
            if head.val < x:
                l1.next = head
                l1 = l1.next
            else:
                l2.next = head
                l2 = l2.next
            head = head.next
        l2.next = None
        l1.next = h2.next
        
        return h1.next